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Cheesyjuggler64
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Joined: 16 May 2024
Posts: 23
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 Posted: Sun Dec 22, 2024 7:51 pm Post subject: how to use a custom initramfs and get a unified kernel image |
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| I have a custom initramfs with busytbox and I want to use it and create a unified kernel image. If its possible I'd like to have it done with install kernel. I've tried to use ukify but I can't get it working. Help appreciated |
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pietinger
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Joined: 17 Oct 2006
Posts: 5234
Location: Bavaria
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| Posted: Sun Dec 22, 2024 8:41 pm Post subject: |
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Although these two pages:
https://wiki.gentoo.org/wiki/Unified_kernel_image
https://wiki.archlinux.org/title/Unified_kernel_image
say that a UKI can have a UEFI boot stub like systemd-stub:
| Quote: | | A unified kernel image (UKI) is a single executable which can be booted directly from UEFI firmware, or automatically sourced by boot loaders with little or no configuration. It is the combination of a UEFI boot stub program like systemd-stub(7), a Linux kernel image, an initrd, and further resources in a single UEFI PE file. |
our developers are of the opinion that it is only a UKI if it has the systemd-stub ...  ... but I don't know how to name a UKI with the kernel's own stub.
I built my “UKI” 5 years ago when the term UKI didn't even exist. Of course I used the kernel's own stub ... and to this day I boot a signed (for SecureBoot) kernel image that contains everything ... it is even a monolithic kernel (=without module support).
Now if you already have a self-made initramfs (like me) then I recommend you to do everything else manually as well, because it's easier than you think (and installkernel is more complicated than you think; I even dont know if it is possible to use an own initramfs).
If you want go the manual route you have to do:
1. Ensure you have in your kernel the CPU microcode built-in (CONFIG_EXTRA_FIRMWARE) and maybe some firmware files if you need it,
2. Option for EFI-stub is enabled in your kernel (CONFIG_EFI_STUB=y),
3. Embedd your external initramfs into the kernel with these settings:
https://wiki.gentoo.org/wiki/User:Pietinger/Tutorials/Initramfs_Overview#Special_Case:_Building_an_embedded_initramfs_with_a_CPIO_archive
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Cheesyjuggler64
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Joined: 16 May 2024
Posts: 23
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| Posted: Sun Dec 22, 2024 9:57 pm Post subject: |
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okay so I've just read the article. So when you're including files they have to also exist within the initramfs file system e.g
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file /sbin/mdadm /root/initramfs/bins/sbin/mdadm 755 0 0
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so the how does this line "This lets the initramfs be built dynamically, always using the latest files from the system" make sense? aren't you still copying the static binaries. Or is it suggesting that you should make a script to create this file? (https://wiki.gentoo.org/wiki/Custom_Initramfs#External_file_list)
Last edited by Cheesyjuggler64 on Sun Dec 22, 2024 10:53 pm; edited 2 times in total |
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Hu
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Joined: 06 Mar 2007
Posts: 22861
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| Posted: Sun Dec 22, 2024 10:49 pm Post subject: |
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| The Wiki is a bit confusing on this point. An initramfs list will always build the initramfs as part of the kernel, using the files specified as sources as they exist at build time. You can choose to specify those files as being pulled from the main filesystem (file /sbin/mdadm /sbin/mdadm 755 0 0 would pull from live), in which case they are always current to your routine updates, or you can choose to pull them from a hand-curated directory that changes only when you want to change it (as shown in the code fragment you posted). The text describes doing the former, but the shown example does the latter. |
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Cheesyjuggler64
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Joined: 16 May 2024
Posts: 23
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| Posted: Sun Dec 22, 2024 10:54 pm Post subject: |
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| ah thanks maybe the wiki could do with some clarification there. Im going to try set it up now. I'm trying to build the initramfs for an encrypted btrfs root. |
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zen_desu
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Joined: 25 Oct 2024
Posts: 57
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| Posted: Mon Dec 23, 2024 12:00 am Post subject: |
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I'm not sure what a UKI helps with if the initramfs is built into the kernel itself.
Are you building that file list outside of the kernel build process?
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